Electrical connectors, such as plugs and jacks, are often connected at opposite ends of multi-wire cables or cords. Subsequent to the connection of the connectors, it is necessary that tests be conducted to determine the integrity of the connections between the individual wires and terminal elements forming parts of the connectors. Recently in the telephone industry, the telephone set has been modulized to permit the rapid installation or removal of cords that run from the telephone handset to the telephone base and cords which run from the telephone set to wall jacks. The cords usually comprise four insulated wires jacketed in a plastic sheath and have plugs with terminal blades or plates electrically contacting the individual wires.
The present invention is concerned in one specific application to a test system for detecting faulty connections between these terminal blades and the individual wires. The test system includes facilities for precisely indicating which terminal blade is not properly in contact with an associated wire.
Through the years numerous test facilities have been developed to test the integrity of connections between contact elements of connectors and individual wires. In addition, these facilities have incorporated means to detect shorts and breaks between wires making up the cable or electrical cord. Invariably, these test facilities included circuits for conducting continuity tests, that is whether a wire will pass or not pass test current. In other instances, the test facilities have included a bridge circuit of one sort or another.
An example of a multiple wire test set is shown in U.S. Pat. No. 3,986,106 issued to E. E. Shuck et al. on Oct. 12, 1976, wherein there is disclosed a test set having facilities for sequentially checking wires having plugs attached to opposite ends. The patent discloses a system which connects distinctive resistors to each wire pair and then executes a comparison test against like resistors mounted in the test set so as to provide an indication of any of a number of faults in the wire pairs, such as lack of continuity, crosses, shorts and reverses between wire pairs. In essence, the test system depends upon the utilization of continuity and resistance comparison tests.
As previously mentioned the prior art is replete with various configurations of bridge circuits for checking wire continuity and determining location of faults in wires making up a cable. Among the more well-known bridge test circuits are the Varley and Murray loops. The Varley loop connects wire pairs as resistance elements in one arm of a Wheatstone bridge to detect the location of a fault such as a ground. The Murray loop test system uses an A.C. bridge having a wire to be tested connected as a distributed capacitance to one arm of the bridge. The test arm of the bridge is matched with an adjustable capacitance arm. By adjusting the capacitance, a match can be made with the distributed capacitance of a wire under test so that an indication may be provided to inform a test operator as to the location of any fault in the wire under test. In general, it should be also noted that the prior art test systems usually require the utilization of significant amounts of current and power.
In testing telephone set cords, it is necessary that the tests be conducted with minute currents, e.g., 10-100 microamps, to insure that the plug contact elements are in good electrical contact with the wires in the cord. Further, there is a need to provide a programmable system for rapidly checking the integrity of wire connections to terminals while at the same time providing an instantaneous indication as to which connections are defective. There are numerous other occasions where there is a need to provide a test system to rapidly indicate the capacitance between a pair of spaced electrically conducting members which may be wire connections, capacitor plates or other spaced electrically conductive members.